/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.remoting.httpinvoker;

import org.apache.http.Header;
import org.apache.http.HttpResponse;
import org.apache.http.NoHttpResponseException;
import org.apache.http.StatusLine;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.entity.ByteArrayEntity;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.PoolingClientConnectionManager;
import org.apache.http.params.CoreConnectionPNames;
import org.springframework.context.i18n.LocaleContext;
import org.springframework.context.i18n.LocaleContextHolder;
import org.springframework.remoting.support.RemoteInvocationResult;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;

/**
 * {@link org.springframework.remoting.httpinvoker.HttpInvokerRequestExecutor} implementation that uses
 * <a href="http://hc.apache.org/httpcomponents-client-ga/httpclient/">Apache HttpComponents HttpClient</a>
 * to execute POST requests.
 *
 * <p>Allows to use a pre-configured {@link org.apache.http.client.HttpClient}
 * instance, potentially with authentication, HTTP connection pooling, etc.
 * Also designed for easy subclassing, providing specific template methods.
 *
 * <p>As of Spring 3.2, this request executor requires Apache HttpComponents 4.2 or higher.
 *
 * @author Juergen Hoeller
 * @see org.springframework.remoting.httpinvoker.SimpleHttpInvokerRequestExecutor
 * @since 3.1
 */
public class HttpComponentsHttpInvokerRequestExecutor extends AbstractHttpInvokerRequestExecutor {

    private static final int DEFAULT_MAX_TOTAL_CONNECTIONS = 100;

    private static final int DEFAULT_MAX_CONNECTIONS_PER_ROUTE = 5;

    private static final int DEFAULT_READ_TIMEOUT_MILLISECONDS = (60 * 1000);

    private HttpClient httpClient;


    /**
     * Create a new instance of the HttpComponentsHttpInvokerRequestExecutor with a default
     * {@link HttpClient} that uses a default {@link org.apache.http.impl.conn.PoolingClientConnectionManager}.
     */
    public HttpComponentsHttpInvokerRequestExecutor() {
        SchemeRegistry schemeRegistry = new SchemeRegistry();
        schemeRegistry.register(new Scheme("http", 80, PlainSocketFactory.getSocketFactory()));
        schemeRegistry.register(new Scheme("https", 443, SSLSocketFactory.getSocketFactory()));

        PoolingClientConnectionManager connectionManager = new PoolingClientConnectionManager(schemeRegistry);
        connectionManager.setMaxTotal(DEFAULT_MAX_TOTAL_CONNECTIONS);
        connectionManager.setDefaultMaxPerRoute(DEFAULT_MAX_CONNECTIONS_PER_ROUTE);

        this.httpClient = new DefaultHttpClient(connectionManager);
        setReadTimeout(DEFAULT_READ_TIMEOUT_MILLISECONDS);
    }

    /**
     * Create a new instance of the HttpComponentsClientHttpRequestFactory
     * with the given {@link HttpClient} instance.
     *
     * @param httpClient the HttpClient instance to use for this request executor
     */
    public HttpComponentsHttpInvokerRequestExecutor(HttpClient httpClient) {
        this.httpClient = httpClient;
    }


    /**
     * Set the {@link HttpClient} instance to use for this request executor.
     */
    public void setHttpClient(HttpClient httpClient) {
        this.httpClient = httpClient;
    }

    /**
     * Return the {@link HttpClient} instance that this request executor uses.
     */
    public HttpClient getHttpClient() {
        return this.httpClient;
    }

    /**
     * Set the connection timeout for the underlying HttpClient.
     * A timeout value of 0 specifies an infinite timeout.
     *
     * @param timeout the timeout value in milliseconds
     */
    public void setConnectTimeout(int timeout) {
        Assert.isTrue(timeout >= 0, "Timeout must be a non-negative value");
        getHttpClient().getParams().setIntParameter(CoreConnectionPNames.CONNECTION_TIMEOUT, timeout);
    }

    /**
     * Set the socket read timeout for the underlying HttpClient.
     * A timeout value of 0 specifies an infinite timeout.
     *
     * @param timeout the timeout value in milliseconds
     * @see #DEFAULT_READ_TIMEOUT_MILLISECONDS
     */
    public void setReadTimeout(int timeout) {
        Assert.isTrue(timeout >= 0, "Timeout must be a non-negative value");
        getHttpClient().getParams().setIntParameter(CoreConnectionPNames.SO_TIMEOUT, timeout);
    }


    /**
     * Execute the given request through the HttpClient.
     * <p>This method implements the basic processing workflow:
     * The actual work happens in this class's template methods.
     *
     * @see #createHttpPost
     * @see #setRequestBody
     * @see #executeHttpPost
     * @see #validateResponse
     * @see #getResponseBody
     */
    @Override
    protected RemoteInvocationResult doExecuteRequest(
            HttpInvokerClientConfiguration config, ByteArrayOutputStream baos)
            throws IOException, ClassNotFoundException {

        HttpPost postMethod = createHttpPost(config);
        setRequestBody(config, postMethod, baos);
        try {
            HttpResponse response = executeHttpPost(config, getHttpClient(), postMethod);
            validateResponse(config, response);
            InputStream responseBody = getResponseBody(config, response);
            return readRemoteInvocationResult(responseBody, config.getCodebaseUrl());
        } finally {
            postMethod.releaseConnection();
        }
    }

    /**
     * Create a HttpPost for the given configuration.
     * <p>The default implementation creates a standard HttpPost with
     * "application/x-java-serialized-object" as "Content-Type" header.
     *
     * @param config the HTTP invoker configuration that specifies the
     *               target service
     * @return the HttpPost instance
     * @throws java.io.IOException if thrown by I/O methods
     */
    protected HttpPost createHttpPost(HttpInvokerClientConfiguration config) throws IOException {
        HttpPost httpPost = new HttpPost(config.getServiceUrl());
        LocaleContext locale = LocaleContextHolder.getLocaleContext();
        if (locale != null) {
            httpPost.addHeader(HTTP_HEADER_ACCEPT_LANGUAGE, StringUtils.toLanguageTag(locale.getLocale()));
        }
        if (isAcceptGzipEncoding()) {
            httpPost.addHeader(HTTP_HEADER_ACCEPT_ENCODING, ENCODING_GZIP);
        }
        return httpPost;
    }

    /**
     * Set the given serialized remote invocation as request body.
     * <p>The default implementation simply sets the serialized invocation as the
     * HttpPost's request body. This can be overridden, for example, to write a
     * specific encoding and to potentially set appropriate HTTP request headers.
     *
     * @param config   the HTTP invoker configuration that specifies the target service
     * @param httpPost the HttpPost to set the request body on
     * @param baos     the ByteArrayOutputStream that contains the serialized
     *                 RemoteInvocation object
     * @throws java.io.IOException if thrown by I/O methods
     */
    protected void setRequestBody(
            HttpInvokerClientConfiguration config, HttpPost httpPost, ByteArrayOutputStream baos)
            throws IOException {

        ByteArrayEntity entity = new ByteArrayEntity(baos.toByteArray());
        entity.setContentType(getContentType());
        httpPost.setEntity(entity);
    }

    /**
     * Execute the given HttpPost instance.
     *
     * @param config     the HTTP invoker configuration that specifies the target service
     * @param httpClient the HttpClient to execute on
     * @param httpPost   the HttpPost to execute
     * @return the resulting HttpResponse
     * @throws java.io.IOException if thrown by I/O methods
     */
    protected HttpResponse executeHttpPost(
            HttpInvokerClientConfiguration config, HttpClient httpClient, HttpPost httpPost)
            throws IOException {

        return httpClient.execute(httpPost);
    }

    /**
     * Validate the given response as contained in the HttpPost object,
     * throwing an exception if it does not correspond to a successful HTTP response.
     * <p>Default implementation rejects any HTTP status code beyond 2xx, to avoid
     * parsing the response body and trying to deserialize from a corrupted stream.
     *
     * @param config   the HTTP invoker configuration that specifies the target service
     * @param response the resulting HttpResponse to validate
     * @throws java.io.IOException if validation failed
     */
    protected void validateResponse(HttpInvokerClientConfiguration config, HttpResponse response)
            throws IOException {

        StatusLine status = response.getStatusLine();
        if (status.getStatusCode() >= 300) {
            throw new NoHttpResponseException(
                    "Did not receive successful HTTP response: status code = " + status.getStatusCode() +
                            ", status message = [" + status.getReasonPhrase() + "]");
        }
    }

    /**
     * Extract the response body from the given executed remote invocation request.
     * <p>The default implementation simply fetches the HttpPost's response body stream.
     * If the response is recognized as GZIP response, the InputStream will get wrapped
     * in a GZIPInputStream.
     *
     * @param config       the HTTP invoker configuration that specifies the target service
     * @param httpResponse the resulting HttpResponse to read the response body from
     * @return an InputStream for the response body
     * @throws java.io.IOException if thrown by I/O methods
     * @see #isGzipResponse
     * @see java.util.zip.GZIPInputStream
     */
    protected InputStream getResponseBody(HttpInvokerClientConfiguration config, HttpResponse httpResponse)
            throws IOException {

        if (isGzipResponse(httpResponse)) {
            return new GZIPInputStream(httpResponse.getEntity().getContent());
        } else {
            return httpResponse.getEntity().getContent();
        }
    }

    /**
     * Determine whether the given response indicates a GZIP response.
     * <p>The default implementation checks whether the HTTP "Content-Encoding"
     * header contains "gzip" (in any casing).
     *
     * @param httpResponse the resulting HttpResponse to check
     * @return whether the given response indicates a GZIP response
     */
    protected boolean isGzipResponse(HttpResponse httpResponse) {
        Header encodingHeader = httpResponse.getFirstHeader(HTTP_HEADER_CONTENT_ENCODING);
        return (encodingHeader != null && encodingHeader.getValue() != null &&
                encodingHeader.getValue().toLowerCase().contains(ENCODING_GZIP));
    }

}
